1. Technical Field
The present invention relates to a liquid crystal device and a method of manufacturing the liquid crystal device.
2. Related Art
Typically, a liquid crystal device is used for a direct view-type display panel, a projector, or a viewfinder of a camera or the like. For example, a liquid crystal device has a configuration in which a liquid crystal layer is confined between a device substrate and a counter substrate. The device substrate has a plurality of pixel electrodes that are provided for respective pixels. The counter substrate has a common electrode that is shared by the pixels. The electric potential of each of the pixel electrodes is alternately switched between a high level and a low level with respect to a common potential on the basis of a drive voltage waveform while the common electrode is held at the common potential, and the liquid crystal layer is alternate current (AC)-driven for each of the pixels. In the case where the liquid crystal layer is driven, an alignment state of the liquid crystal layer is changed, and a polarization state of light that passes through the liquid crystal layer changes in accordance with the alignment state of the liquid crystal layer. The light that has passed through the liquid crystal layer is partially absorbed by a polarization plate in accordance with the polarization state with the result that light exhibiting a desired gray scale is produced, thereby contributing to displaying of an image.
In the case where a voltage is not applied, the alignment state of the liquid crystal layer is regulated by an alignment layer such as an organic alignment layer or an inorganic alignment layer. An inorganic alignment layer that is formed by a sputtering method or a vapor deposition method is superior to an organic alignment layer in terms of improvement of light resistance. Examples of a liquid crystal device in which an inorganic alignment layer is used include one of a type disclosed in JP-A-2009-210766.
In the liquid crystal device disclosed in JP-A-2009-210766, an inorganic alignment layer including a plurality of vapor-deposited layers is used. One of the vapor-deposited layers functions as an alignment layer that is formed so as to contact a liquid crystal layer. Another vapor-deposited layer is formed as the bottom layer at a deposition angle of 90°. The bottom vapor-deposited layer has a precise configuration, and therefore the reliability of the alignment layer can be enhanced.
In the case where imbalance is caused between the rise and fall of an effective voltage waveform with respect to a common potential, such imbalance causes a flickering, image burning, or the like, the effective voltage waveform being applied to the liquid crystal layer. The following mechanism is thought to be a cause of the imbalance between the rise and fall of the effective voltage waveform.
In general, a structural difference is provided between the side of the device substrate and the side of the counter substrate. A force with which impurities (such as impurity ions, especially) contained in the liquid crystal layer are attracted to the side of the device substrate is asymmetric to a force with which the impurity ions are attracted to the side of the counter substrate, each of the forces acting on the liquid crystal layer. Accordingly, the impurity ions are nonuniformly adsorbed to the side of the device substrate or to the side of the counter substrate, and the adsorbed impurity ions affect an electric field with the result that the effective voltage waveform is shifted. Consequently, a predetermined common potential becomes inadequate in terms of balance between the rise and fall of a voltage waveform.
For example, in order to overcome such a disadvantage, a technique disclosed in JP-A-2005-49817 can be employed. A reflective liquid crystal display device disclosed in JP-A-2005-49817 has a pixel electrode made of a light reflective material and has a common electrode made of light transmissive material. A work function-adjusting layer having a work function larger than that of the common electrode is formed on the pixel electrode. A work function obtained as a result of adding the work function of the pixel electrode to that of the work function-adjusting layer is configured so as to approach the work function of the common electrode.
In the technique disclosed in JP-A-2005-49817, imbalance between the rise and fall of the effective voltage waveform is assumed to be able to be precluded owing to a difference in the work functions between the pixel electrode and the common electrode. However, there is still room for improvement as described below.
For example, even in the case where the pixel electrode is made of the same material as the common electrode, nonuniformity of the impurity ions in the liquid crystal layer is caused. Namely, the nonuniformity of the impurity ions is generated resulting from causes other than the difference in the electrode materials, and therefore the technique disclosed in JP-A-2005-49817 has limitations regarding prevention of the nonuniformity of the impurity ions. Furthermore, the formation of the work function-adjusting layer causes disadvantages, such as the adjustment of the work function causing adverse effects on the electrical properties or display properties of the liquid crystal device, the device configuration becoming complicated, and the increased number of manufacturing processes causing decreased manufacturing efficiency.